Elevators typically have a suspension roping between the elevator car and the counterweight which roping passes around a rope wheel mounted stationary in some suitable position above said elevator units. Additionally, the elevator may need to be provided with a second roping between the elevator car and the counterweight suspended to hang from the elevator car and the counterweight. This type of arrangement is normally used to provide compensation for the weight of the hoisting roping. Particularly, in this way the unbalance caused by the hoisting roping and occurring when the elevator car is run to its extreme position can be eliminated. The second roping can additionally or alternatively be used to provide a tie-down-function (also known as lock-down function). The second roping is generally tensioned to pass around a rope wheel mounted stationary in some suitable position below said elevator units, for instance in the lower end of the hoistway.
When an elevator car is parked at landing to unload and load, people tend to move within the car and between the car and the landing such that car load is uncontrollably changed. In particular, in these situations people are generally free to exit and enter the elevator car as they wish. In these situations more or less sudden vertical forces, often affecting the car in an impact-like manner, are exerted randomly on the elevator car. Correspondingly, sudden lightening of the load causes sudden changes in vertical forces exerted on the car.
Unless prevented, the sudden changes in vertical forces are likely to cause rapid stepwise movement of the car upwards or downwards, or even vertical swinging of the car. A drawback of the known elevators has been that this kind of rapid movement of the car caused during the loading and unloading has been difficult to eliminate simply and efficiently.
The second roping may be furthermore tensioned with a tensioning means, such as a tensioning weight. In a sudden increase of car load, the car is displaced downwards whereby the second roping is momentarily loosened. The tightening arrangement rapidly returns the higher tension level back to the second roping, whereby it urges the car to the same direction as the increased load.
The tie-down function, referred to above, is usually obtained by arranging the second roping to pass around a rope wheel. Considerable rising of the rope wheel in a case where the counterweight (or the car) accidentally comes to a sudden stop during a run of the elevator, is blocked and therefore the rope wheel can produce a support force for the loop of the second roping so it restricts the elevator car (or counterweight, respectively) from continuing its upwards directed movement, i.e. so called jumping is prevented. Such a sudden stop may be caused for example if during a run of the elevator the counterweight accidentally gets stuck on its guide rails or if the safety gear is activated, e.g. due to overspeed situation. These types of incidents would be harmful and dangerous, because they would cause sudden jerks for the people inside the car. One sort of a tie-down arrangement is disclosed in U.S. Pat. No. 2,270,441 A, for instance. The known tie-down devices generally react to extremely large one-directional shocks caused in the elevator roping system during an emergency, and they are not designed solve the problems of the loading and unloading situations. In particular, they are not suitable to act as means for removing up and down-directed fine-scale jerks caused in the car during a normal situation, when an elevator car is parked at landing for unloading and/or loading.